1. Field of the Invention
The present invention relates to a fabrication method for a fluid injection micro device, and more particularly, to deep silicon etching and polishing method for a fluid injection micro device.
2. Description of the Related Art
An ink-jet printhead is a key component of a color ink-jet printer. The Ink-jet printhead comprises an upper plate, an intermediate dry film, and a lower plate. The upper layer comprising an ink nozzle may be composed of noble metal (e.g., Cu, Au, Ni, or Ni—Au alloy), glass, or plastic. The lower plate is a thermally stable substrate, such as a silicon wafer, having microelectronic circuits thereon. The intermediate dry film is lithographed and etched to define an ink passageway.
FIG. 1 is a schematic diagram of a conventional fluid injection micro device. Referring to FIG. 1, a fluid injection micro device is formed on a substrate 10 (e.g., silicon wafer). A dielectric layer 20, such as silicon oxide, is formed on the substrate 10. The dielectric layer 20 may be deposited using a CVD process. A patterned resistive layer 30 is formed on the dielectric layer 20 as a heater. The resistive layer 30 comprises HfB2, TaAl, TaN, or TiN. The resistive layer 30 may be deposited using a PVD process, such as evaporation, sputtering, or reactive sputtering. Next, a patterned conductive layer 40, such as Al, Cu, or Al—Cu alloy, is formed overlying the dielectric layer 20 and covers the heater 30 to form a signal transmitting circuit. The conductive layer 162 may be deposited using a PVD process, such as evaporation, sputtering, or reactive sputtering. Thereafter, a protective layer 50 is formed using a CVD process to isolate the ink and the heater.
Thereafter, a thick film 60 is formed on the protective layer 50. The thick film 60 is composed of polymer material, such as polyimide, is formed around a fluid chamber 70 containing ink. After formation of a manifold and attachment of a plate 80, the substrate is bonded onto a flexible printed circuit board. The nozzle plate 80 comprises an electroplating plate or a flexible printed circuit board. According to this conventional method, the heating element 30 is beneath the orifice 90. The inkjet droplet is ejected from the fluid chamber 70 by pullback force. It is difficult to inhibit unstable ink conditions which result in satellite droplets. For example, ink close to the orifice can overflow, or the tail of an ink droplet may not be cut off properly. The tiny ink droplets that trail the main droplets, known as satellite droplets, may hit the paper at locations slightly different than the main droplets and blur the printed image. Moreover, in order to accurately align the heating element 30 and the orifice 90, either the electroplating plate or a flexible printed circuit board is required, thus, manufacturing costs are increased.
U.S. Pat. No. 6,102,530 discloses a method of a fluid injection micro device using a wet etching process. Referring to FIG. 2, a fluid injection micro device comprises discharge resistors, such as the first heater 130a and second heater 130b, placed on opposing sides of the orifice 132 possess different resistances and are electrically connected to a common electrode (not shown) for activating the ink in the associated chamber 170.
After a common electrical pulse is applied, the first heater 130a and second heater 130b are activated simultaneously. Due to the resistance difference, the first heater 130a, having a narrower cross-section, is activated more quickly and generates a first bubble 180a. The expanding first bubble 180a begins to restrict the ink flow to the manifold 160, and finally functions as a virtual valve to isolate the chamber 170 and to prevent the adjacent chambers from cross talk. Then, a second bubble 180b is formed by the second heater 130b. As the second bubble 180b expands and approaches the first bubble 180a, the ink is pressurized by the first bubble 180a and the second bubble 180b and is ejected through the orifice 132. However, it is critical to control the construction of the support layer, in order to meet high production yield and durability requirements.